Randomized controlled trials of split virus vaccines in healthy adults have not been able to detect an increase in systemic adverse events compared to control vaccination. These trials do identify a non-trivial risk of systemic symptoms occurring in the week after both placebo and vaccine. There is a small population of healthcare workers who report consistent systemic symptoms after split virus vaccination which may occur because a small group of healthy adults have true physical reactions to components of the vaccine or excipients. If this is true, then alternatives - such as the use of subunit vaccines or live attenuated nasal spray vaccines - might be expected to be better tolerated by these people.